The present invention relates generally to electronic systems having a standby mode to minimize current drain, and more particularly to a wake-up circuit for an electronic system and method therefor for use in telematics communication system.
Mobile or portable electronic systems, such as a telematics communication system, are typically powered by a portable power supply, such as a battery in an automotive vehicle, and have full functionality in a normal operating mode. Such electronic systems commonly have a standby mode to minimize current drain on the battery when the electronic system is turned on but not requiring the full functionality in the normal operating mode. Hence, the standby mode permits low power or current consumption to support reduced or minimum functionality of the electronic system while the normal operating mode permits normal operating power or current consumption to support full functionality of the electronic system. Typically, an electronic system has a normal mode power supply to provide power to the electronic system when operating in the normal operating mode and a separate standby mode power supply to provide power to the electronic system when operating in the standby mode.
An electronic system is known to xe2x80x9cwake-upxe2x80x9d when the electronic system changes from the standby mode to the normal operating mode responsive to a wake-up signal. A wake-up signal may be generated when a user activates a switch, such as a pushbutton or a key. In some electronic systems it is important that the electronic system wake-up almost instantaneously to give an impression to a user that the electronic system was always in the normal operating mode and to instantaneously provide the full functionality associated with the normal operating mode.
When the pushbutton is used as the switch to generate the wake-up signal, a relatively high level of current must pass through its conductive contacts to overcome or break through any electrical resistance caused by contamination or oxidation that may be present on the conductive contacts.
Further, when the pushbutton is located at a remote position relative to control circuitry of the electronic system and electrically coupled to the control circuitry of the electronic system using a wire, then the electronic system must be able to determine the electrical state of the switch or the wire indicating a failure thereof. The detection of the electrical state-of the switch or the wire is especially needed when the pushbutton serves a critical function, such as an emergency call button in the telematics communication system.
One known technique for the processor to determine the electrical state of the switch is using a resistor-based circuit. In this case, a resistor is connected in parallel with a switch. A first terminal of the resistor is connected to ground. A second terminal of the resistor is connected to a direct current (DC) voltage. An analog to digital (A/D) input port to the processor monitors the DC voltage at the second terminal of the resistor. The processor interprets a low voltage (e.g., 0 V) at the AID input port as an active state, wherein the switch is pressed or closed. The processor interprets a mid voltage (e.g., 2.5 V) at the A/D input port as an idle state, wherein the switch is not pressed or open. The processor interprets a high voltage (e.g., 5 V) at the A/D input port as a failure state, wherein a wire connecting the switch to the processor is broken or open. However, there are several disadvantages of the resistor-based circuit. The resistor-based circuit is relatively complex and therefore, relatively expensive to implement. The resistor-based circuit draws a steady amount of current that drains a battery power supply such that the switch practically can only be used when the electrical system is turned on, since the standby current drain is too high. Further, the resistor-based circuit cannot detect a short circuit state, wherein the switch is stuck in a closed position.
Accordingly, there is a need for a wake-up circuit for an electronic system and method therefor that uses a minimum amount of current while the electrical system is in the standby mode, that delivers a relatively high level of current to the switch during wake-up, and that determines the electrical state of the switch or the wire in the remotely positioned switch or in the wire leading to the remotely positioned switch.